The present invention relates to an apparatus for extracting a hot gas sample from a chamber and for feeding the sample to an analyzer, in particular for monitoring the content of organic solvents or similar constituents in the air in the chamber, which such solvents or similar constituents represent an explosion hazard or are otherwise harmful when they reach a specific concentration, such apparatus comprising a sampling probe which can be introduced into the chamber through an opening in the chamber wall and is connected outside the chamber with the analyzer, which has a gas filter and a detector, there being a suction pump to draw off the sample through the probe to the analyzer, as well as a heating jacket upstream of the analyzer.
Such apparatus is already known, in which the rear end of the probe is connected outside the chamber via a flexible hose with the analyzer, which is located at least 5 to 30 meters away from the site where the sampling probe passes through the chamber wall. The heating jacket surrounds the hose connecting the probe with the analyzer.
In this known configuration, it is a disadvantage that the gas sample cannot be prevented from cooling down, despite the heating jacket, on its way from the chamber to the analyzer, resulting in the condensation of such constituents in the sample as saturate or nearly saturate the air in the chamber. This condensation which takes place upstream of the analyzer leads to the analyzer results not reflecting the actual conditions in the chamber, so that an existing explosion hazard may not be recorded and taken into account. In addition, the deposit of condensate may even lead to the passage for the gas sample becoming blocked, so that measurements cease altogether. The heating jacket provided for the connecting hose can counteract these hazards only to a limited extent. The temperature of the gas sample first drops in the zone of the passage through the chamber wall. Particularly the screw couplings for joining the connecting hose to the sampling probe, on the one hand, and to the analyzer, on the other hand, constitute cold sites, however, where there is an enhanced risk of condensation. This is especially so, when the temperature in the chamber, and thus of the gas sample, is high at 250.degree. C. or more, a temperature drop of some 80.degree. C. having been recorded at the cold sites. Under such conditions, substantial condensation of constituents with a high boiling point can be reckoned with in the sample.
Another disadvantage of the known configuration is the time lag with which the analyzer records changes in concentration inside the chamber. If the suction pump has a normal throughput of 3 1/min and the internal diameter of the hose connecting the sampling probe with the analyzer is 4 mm, the retention time is approx. 2.4 secs per meter of the connecting hose. For a connecting hose 15 meters long, for instance, the time lag in the measurements is as much as 36 secs. something which is unacceptable in monitoring a process involving an explosion hazard.
From U.S. Pat. No. 2,648,976 of Bur, a method is known of connecting a gas sampling tube by a short flexible conduit to an analyzer, the flexible conduit serving to make it possible to shift the receiving end of the sampling tube extending into the chamber through which gas to be sampled is passing, in order to withdraw gas samples at points over the cross section of the chamber, the angular length of tube inside the chamber being moved to and fro within an arc for this purpose and also being shiftable axially. In this case, however, the analysis of furnace gases is involved, heating or insulating apparatus being employed neither with the sampling tube nor with the flexible conduit nor with the analyzer. For this reason, the withdrawn gas sample suffers a considerable drop in temperature in this case too, despite the analyzer being not far away from the chamber, so that condensation must likewise be reckoned with and accordingly distorted sampling analysis when the gas sample has an appropriate composition.
From the U.S. Pat. No. 3,793,887 of Anderson et al., a method is also known, in testing the exhaust of internal combustion engines, of extracting a gas sample by means of a probe introduced into the exhaust duct, the probe being connected to an expandable collection bag for the sample, the bag being in an enclosure and there being separate heating apparatuses for the probe and for the enclosure. This known system serves, however, solely to obtain a gas sample representative of actual conditions over a fairly long running time for the engine, a pump being intended to maintain in the collection bag an instantaneous pressure equal to the instantaneous pressure at the exit to the exhaust duct. Consequently, there is no analyzer in the heated enclosure, the exhaust gas sample instead being analyzed outside the heated enclosure after termination of the lengthy period of sample extraction, so that condensation and incorrect analysis figures are involved in this case too, in the event that the extracted gas sample contains vapours. Moreover, there is no insulation for the sampling probe and the heated enclosure.